NOTE: As their name suggests hints are not exactly The Walking Dead: Survival Instinct cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing The Walking Dead: Survival Instinct even more entertaining.

Relics
Bigger Clips: Complete the game once with Mia in your party
Crossbow/Assault Rifle: Complete the game once, you'll be able to use these from the beginning of the game.
Faster Stronger: Complete the game once with Sheila in your party.
Item Boost: Complete the game once with Swenson in your party.
Marksman Boost: Complete the game once with Harrison in your party.
Melee Boost: Complete the game once with Jane in your party.
Silenced Weapons: Complete the game once with Blake in your party.
Stealth Movement: Complete the game once with Warren in your party.
Survivor Success: Complete the game once with Noah in your party
Unlimited Ammo: Unlock every relic(perk) to unlock this.

Achievements
Been Everywhere (50): Complete All Marked Destinations on the Map
BOOM! Who Needs a Headshot? (15): Kill 5 Walkers with One Explosion
Crash Course in Brain Surgery (25): Kill 100 Walkers while Grappling
Down to My Last (15): Complete the Game with Only 1 Firearm and 1 Bullet Left in Your Inventory
Duct Tape Can Fix Anything (10): Survive 5 Breakdowns
Every Man, Woman and Child (30): Choose to Travel at Least Once with Every Optional Survivor
Extreme Conditioning (10): Sprint Until You're Exhausted 10 Times in One Level
Get Out of Dodge (30): Complete the Final Marked Destination on the MapGood Samaritan (30): Complete 25 Optional Objectives
Group Hug (5): Kill 4 Walkers in a Single Grapple Sequence
Guys Night Out (20): Arrive at Final Destination with Only Male Survivors
Have a Nice Trip! (20): Kill a Walker That Is Falling Due to Dismemberment
I Can Handle This Myself (30): Enter Sherwood Without Any Survivors
I Used to Be a Human Like You (5): Shoot a Walker in the Knee with a Bolt
It's Gotta Be the Brain (45): Dismember All Limbs of 5 Walkers
It's Not Venison, but It'll Do (10): Consume 50 MREs
Mind if I Borrow This? (15): Pull a Bolt From a Walker Then Kill Them With It
Moving to the 'Burbs (20): Complete the Third Act
Need a Hand? (5): Prevent a Walker from Damaging You by Severing Its Attacking Limb
Need More Spots Up Front (35): Dismember 250 Limbs
Next Step: Bullet Belt (15): Fire 300 Bullets
No Down Payments (30): Find Every Useable Vehicle
No Stone Left Unturned (50): Collect Every Stuffed Squirrel
Nobody Can Kill Merle but Merle (15): Complete the Second Act
Not a Scratch (30): Complete a Marked Destination on the Map without Taking Any Damage
Now Don't You Get Bit! (30): Prevent 50 Walkers from Grabbing You
Oedipal Complex (5): Complete the First Location
On the Road Again (5): Explore an Unmarked Travel Location
Ooh, Shiny! (15): Distract 50 Walkers with Items
Porcupine (15): Shoot a Walker with 10 Bolts without Killing It
Rosie the Rampager (20): Arrive at Final Destination with Only Female Survivors
Say Hello to My Little Friend (10): Complete a Marked Map Destination Using Only Firearms
Sneak Attack (35): Perform Execution Kills on 50 Walkers
Sorry, Brother (10): Complete the First Act
Stay Together, Stay Safe (10): 5 Survivors Were Killed While Scavenging
Still Not Buying a Hybrid (10): Consume 250 Fuel
That Looks Like It Hurt (30): Restore Survivors 25 Times
That's a Nice Swing You've Got (15): Kill Walkers Using Every Melee Weapon
The Hunted Becomes the Hunter (10): Killed 5 Walkers in the Cabot Ridge Creek Bed
The Missing 8 (50): Find Every Poster
They Know Me at the Range (15): Kill Walkers Using Every Ranged Weapon
They're People, Too! (30): Complete a Marked Destination on the Map without Killing a Walker
This Is How Hot Dogs Are Made (10): 10 Walkers Killed with Saw Blades in the Logging Camp
True Dixon (25): Complete a Marked Destination on the Map Using Only the Crossbow
Two Heads Are Better Than One (5): Kill Multiple Walkers with One Bullet
We Survive by Pulling Together (5): Recruit 1 Optional Survivor
You're Doing It Wrong (10): Perished 13 Times
You're Just Not My Type (10): Complete a Marked Destination on the Map without Being Grabbed by a Walker
Zig-Zagging All Over the Road (50): Explore 25 Unmarked Travel Locations